Film scanners are appliances in which the film is scanned optically in order to obtain video signals which can be processed, transmitted or stored once again. Various physical forms have become known for this purpose. In one of these physical forms, the film is imaged for colour scanning by means of a suitable objective and a colour splitter onto three line sensorsxe2x80x94also referred to as CCD sensors. The images are then scanned line-by-line by moving the film, with the scanning in the line direction being carried out by clocked reading in the individual elements of the line sensor.
Convergence errors, which are also referred to as registration errors and which can be seen in the form of coloured edges when the video signals are reproduced, can occur between the three primary colours red, green and blue as a result of tolerances of the optical elements and inaccuracies in the mounting of the line sensor on a holder.
The object of the present invention is to provide an apparatus which allows very accurate fine adjustment of the position of the images on the line sensors.
This object is achieved according to the invention in that a glass pane is arranged between in each case one outlet surface of a colour splitter and the respective line sensor and can be pivoted in two directions out of a plane lying at right angles to the beam direction, so that the light emerges offset from the glass pane as a function of the pivoting angle.
The invention has the advantage that the three primary colours of a film image are set in position with pinpoint accuracy, and can thus be made to coincide. A further advantage is that the apparatus according to the invention can not only be produced at low cost, but is also temperature-stable.
One advantageous refinement of the invention consists in that depending on the pivoting direction, the glass pane is mounted on two contact points in a housing, and the pivoting directions are essentially at right angles to one another, with one contact point being provided jointly for both pivoting directions. The position of the three primary colours can thus be adjusted independently of one another in the horizontal and vertical directions.
One advantageous embodiment of the invention consists in that the glass pane is held firmly in a metal plate which can pivot and has an incline for each pivoting direction, on which incline an adjusting screw, which is arranged in a housing, acts against the force of a spring force which acts between the metal plate and the housing. In addition to the already mentioned advantages, this embodiment is distinguished by the fact that the adjusting screws are easily accessible and can be operated from a direction at right angles to the respective optical axis.
A further advantageous refinement of the apparatus according to the invention not only allows the positions of the images to be adjusted, but also allows adjustment of the focusing for each individual line sensor, in that the line sensor is arranged on a mount which can pivot about an axis parallel to the lines. In this refinement as well, easy accessibility to the adjusting screws can be achieved in that the mount is provided with an incline on the side of the line sensor opposite the pivoting axis, on which incline an adjusting screw acts against a spring force.
A further requirement for correct scanning of the film images is that all the line sensors are at the same angle, which means that the respectively scanned lines are parallel to the frame line. In order to correct any errors relating to this, one development of the invention provides that the line sensor is arranged on the mount by means of a sensor holder, in that the sensor holder has two pins in an extension of the longitudinal axis (line direction) of the line sensor, which pins project into holes in the mount and have play at right angles to the line direction, and in that an adjusting screw projects from each of the two sides into the hole.
One of the pins is defined as a reference point with respect to the line. In order that this pin is located in the correct position in the line direction when it is inserted into the mount, the development can be triggered such that the pins are flattened on one side.